taken 12 years ago, near to Kinnesswood, Perth And Kinross, Great Britain

Thermals over Bishop Hill providing lift to gliders

Warm air rising in front of and above the hill allow glider pilots to stay up for hours.
These thermals are the escalator or lift to the heavens.
More about these atmospheric phenomena here: Link

My thanks to James Allan for his input here: Gliders usually operate here in orographic up-currents or mountain waves, caused by westerly winds being forced upwards by the Bishop Hill escarpment. Thermals (as described in the link) can occur here too under certain conditions, but were probably absent under the cloud cover depicted.

There are ten gliders in this picture above this gridsquare, sometimes there can be more.
From the ground it looks like a wartime dog-fight Link